In the prior art, techniques for measuring the spin of a spherical body such as a ball are proposed. For example, Patent Literature 1 and 2 adds a sensor to a ball and Patent Literature 3 photographs a marker-attached ball with a camera to obtain information of the ball such as the number of spins, the spin rate, the spin period, and the direction of the spin axis.
Besides, in ball sports such as baseball, the moving speed of a ball is widely measured simply by using a device called the speed gun.